Remark 2.18: The main point of this theorem is that for a negative integral
class \(z\in H^{1,1}(M)\) , the orthogonal hyperplane either passes
through the interiour of some Kähler-Weyl chamber and then it contains no face of a Kähler-Weyl chamber
(that is, \(z\)  is not
MBM), or its
intersection with the positive cone is a union of faces of such
chambers (when \(z\)  is MBM). This is illustrated by a picture
taken from [1]}:
